Plate heat exchanger

ABSTRACT

A plate heat exchanger (1) comprises a stack of heat transfer plates (2) provided between two end pieces (3, 4) and each having an essentially plane extension. Each end piece (3, 4) has an inner surface (9) facing said heat transfer plates and an outer surface (14) facing away from said heat transfer plates (2) and extending from one side to another of the end piece (3, 4). The plate heat exchanger (1) is compressed by means of at least one member (18) extending around the plate heat exchanger and abutting said outer surface (14) of each end piece (3, 4) in order to prevent the retreat of the end pieces from each other. The outer surface (14) of each end piece (3, 4) is curved in such a manner that the end piece has a convex shape in a cross section along a first plane (Y, Z) being perpendicular to the essentially plane extension of the heat transfer plate (2).

TECHNICAL FIELD OF THE INVENTION AND PRIOR ART

The present invention refers to a plate heat exchanger comprising astack of heat transfer plates provided between two end pieces and eachhaving an essentially plane extension, each end piece having an innersurface facing said heat transfer plates and an outer surface facingaway from said heat transfer plates and extending from one side toanother of the end piece, the plate heat exchanger being compressed bymeans of at least one member extending around the end pieces and theheat transfer plates in such a manner that said member abuts said outersurface of each end piece in order to prevent the retreat of the endpieces from each other.

A conventional plate heat exchanger comprises a stack of heat transferplates being compressed between two end pieces or end plates by means oftwo or more bolts or tightening bars. The bolts extend between holesextending through the end plates in their outer regions and outside thestack of heat transfer plates compressed between the end plates. Theinternal pressure of the heat exchanger acts on the end plates and sincethe bolts are located outside the pressure-loaded surface of the endplates, there are large bending stresses in the end plates, which mayresult in a considerable deflection of the end plates. Such a deflectionleads to a play in the plate stack, which in turn influences the thermalperformance and, to a certain degree, also the fatigue strength of theplates. To compensate for this it is necessary to use end plates havinga significant thickness of material already by relatively moderateworking pressures. Consequently, the plate heat exchanger becomes heavyand the manufacturing cost is relatively high.

JP-A-62 062 186 discloses a plate heat exchanger of the initiallydefined type, comprising a stack of heat transfer plates providedbetween two end plates. Each end plate comprises a planar inner surface,facing the heat transfer plates, a planar outer surface, and edgesurfaces connecting the inner and outer surfaces. A compressing memberin the form of a belt-type thin sheet extends around the plate heatexchanger. Said sheet is sharply bent around the corners formed by theouter surface and the edge surfaces. Due to this sharply bent cornersthe inherent stresses in the compressing are not negligible. Moreover,bending stresses will exist in the end plates, resulting in a deflectionof the end plates in a central portion thereof. Consequently, the plateheat exchanger disclosed in JP-A-62 062 186 is not able to withstandhigh internal pressures.

In comparison to this Japanese prior art, JP-A-62 062 187 discloses asomewhat modified plate heat exchanger comprising longitudinal ribsprovided on the outer surface of the end plates. The thin sheet of thecompressing member extends around the plate heat exchanger and abuts astraight edge surface of the ribs in such a manner that the thin sheetis bent around the ribs. As in JP-A-62 062 186, the thin sheet issharply bent around the corners of the end plates.

SE-B-343 383 discloses a plate heat exchanger having a stack of heattransfer plates provided between two end pieces, each end piececomprising a curved outer surface facing away from the heat transferplates and a plane inner surface facing the heat transfer plates. Thecurved outer surface has a dome-like shape, i.e. it is curved in alldirections. Furthermore, each end piece is provided with acircumferentially extending flange having holes through which tighteningbolts extend for keeping together the plate heat exchanger stack. Inaddition, one of the end pieces comprises a plate forming the planeinner surface and being hydraulically movable against the heat transferplates in order to press these together.

SE-B-413 695 discloses packages of heat exchanger plates, said packagesbeing intended to be placed in chambers of rotating heat exchangers. Theheat exchanger packages are temporarily compressed by a band forfacilitating the insertion of the packages in the chambers. When theheat exchanger packages are positioned in the rotating heat exchangerthe bands are cut and the packages are allowed to expand in radialdirection in the chambers. Thus, the bands are not suitable forcompressing the heat exchanger package when it is subjected to thepressure of the flowing medium.

GB-A-2 151 347 discloses a plate heat exchanger with a plurality of heattransfer plates being enclosed between a base and a closure memberintegrally connected to the base by side walls to form a circumferentialframe. A movable plate is insertable between the closure member and theheat transfer plates. The heat transfer plates are pressed against eachother by moving the movable plate from the closure member by means oftightening screws in the direction of the base.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a plate heat exchangerwhich is compressed in such a manner that the bending stresses in theend pieces may be reduced. This object is obtained by the plate heatexchanger initially defined and characterized in that said outer surfaceof each end piece is curved in such a manner that the end piece has aconvex shape in a cross-section along a first plane crossing said sidesand being perpendicular to the essentially plane extension of the heattransfer plate. Due to such a curved outer surface of the end pieces,the circumferentially extending compressing member may effectivelyresist the internal pressure forces. By means of the compressing memberaccording to the present invention, the internal pressure in the heatexchanger is transferred to the curved end pieces as uniformlydistributed pressure stresses. Thereby, no significant bending momentwill occur and no significant deflection of the end pieces will takeplace. The end pieces essentially function as distance members andconsequently may be manufactured in a material with lower strength thanrequired according to the prior art.

According to an embodiment of the present invention, said outer surfaceof each end piece is continuously curved from said one side to another.Such a continues curvature enables minimizing of the stresses in the endpieces.

According to a further embodiment of the present invention, the curvedouter surface in the proximity of an edge between said inner surface andsaid outer surface is shaped in such a manner that a tangential plane ofsaid outer surface is essentially perpendicular to the essentially planeextension of the heat transfer plate. In such a way, a sharp bending ofthe compressing member is avoided, which otherwise might have resultedin bending stresses in the end pieces, or in strength problems of thecompressing member.

According to a further embodiment of the present invention, thecompressing member comprises joining means provided to releasablytighten the compressing member around the end pieces and the heattransfer plates. Furthermore, said joining means may be provided toenable adjustment of the compressing force of the compressing member.

According to a further embodiment of the present invention, thecompressing member comprises at least one wire-, bar-, band- orplate-like member extending around the end pieces and the heat transferplates. Thereby, the compressing member may comprise at least one boltextending in a loop in such a manner that it is closely abutting atleast one of the curved outer surfaces of the end pieces. Furthermore,the compressing member may comprise at least a pair of curved boltsmutually connected to a loop and each being curved in such a way thatthey are closely abutting the curved outer surface of a respective endpiece in a common plane. Advantageously, the joining means may comprisea nut having a right-handed thread and a left-handed thread and beingscrewed onto opposite bolt ends. Alternatively, the compressing membermay comprise a wire being wound in a helical coil about the end piecesand the heat transfer plates. Advantageously, the helical wire coil iswound in such a way that each round of the wire is abutting theadjoining wire round. According to still a further alternative, thecompressing member comprises a plate which extends around the end piecesand the heat transfer plates. Such a plate may for instance have thesame width as the plate heat exchanger. Moreover, the plate may bedivided in two parts, each part may extend around a respective end piecein such a way that each end edge of one part is adjacent to an end edgeof the other part, and adjacent end edges of the parts may be joined toeach other by the joining means.

According to a further embodiment of the present invention, each endpiece comprises a plane plate forming said inner surface. Thereby, eachend piece may comprise a support plate disposed on the plane plate andhaving a curved edge surface. Advantageously, the support plate extendsessentially perpendicularly to the plane plate. Moreover, several suchsupport plates may be provided and spaced from each other, and a furthersupport plate may extend essentially perpendicular to the support platesin order to support the support plates in the lateral direction.

According to a further embodiment of the present invention, said convexshape is essentially semicircular. By a semicircular curvature of theend pieces essentially all bending stresses thereof may be eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained more closely by means ofdifferent embodiments disclosed in the drawings attached hereto.

FIG. 1 is a sectional view through a heat exchanger according to a firstembodiment.

FIG. 2 is another sectional view through the heat exchanger.

FIG. 3 is a partly sectional side-view of the heat exchanger accordingto a second embodiment.

FIG. 4 is another side-view of the heat exchanger in FIG. 3.

FIG. 5 is a view from beneath of a plate heat exchanger in FIG. 3.

FIG. 6 is a view from above of the heat exchanger in FIG. 3.

FIG. 7 is a sectional view through a further embodiment.

FIG. 8 is an enlarged sectional view of a detail in FIG. 7.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS

FIG. 1 discloses a first embodiment of a plate heat exchanger 1according to the present invention. The plate heat exchanger 1 comprisesa stack of heat transfer plates 2 being corrugated and compressedagainst each other between two end pieces 3 and 4. One 3 of the endpieces comprises inlet and outlet means 5 for a first and second,respectively, medium carried through channels 6 and 7, one for eachmedium, and formed between the heat transfer plates 2. For sealing offthe channels 6 and 7 gaskets 8, preferably of rubber, are providedtherebetween. It should be noted, however, that the channels 6, 7 may bepermanently sealed off as well by any suitable method, such as welding,brazing, gluing or the like. Moreover, the heat transfer plates 2 may bepermanently fixed together in pairs, such pairs then being arranged insaid heat transfer plate stack. Each heat transfer plate 2 has anessentially plane extension in a longitudinal direction X and adirection Z orthogonal to the direction X, and a small height in adirection Y in relations to the plane extension. Each heat transferplate 2 has a normal with respect to the essentially plane extension andthe heat transfer plates 2 are arranged in such a way that their normalsare essentially parallel.

Each end piece 3 and 4 has, as disclosed in the sectional view of FIG.2, a plane inner surface 9 facing the heat transfer plates 2 and acurved outer surface 10 facing away from the heat transfer plates 2. Thecurved outer surface 10 has a convex, oval shape in a cross-section. Theoval shape has no sharp corners and the curved outer surface 10 is, inthe proximity of an edge between the inner surface 9 and the outersurface 10, i.e. at the junction to the plane inner surface 9,perpendicular to the essentially plane extension of the heat transferplate 2, i.e. extends in the height direction Y. It should be noted thatalso other curved surface shapes are suitable, for instance semicircularor elliptic.

In order to compress the plate heat exchanger 1 a flexible, bendablecompressing member, in the example disclosed a wire 11, is wound aroundthe end pieces 3 and 4 and the heat transfer plates 2 lyingtherebetween. Preferably, the wire 11 is manufactured in a material ofhigh strength. The wire 11 is wound as a helical coil around the endpieces 3, 4 and the heat transfer plates 2 in such a manner that eachround of the wire 11 is closely abutting the adjoining wire round. Thewire 11 is tightly wound along the complete length of the plate heatexchanger 1, one end of the wire 11 being fixed to one of the end pieces3, 4, and the other end of the wire 11 being fixed to one of the endpieces 3, 4. Due to the curved shape of the end pieces 3 and 4 noessential bending stresses will occur therein but mainly pressurestresses. Said pressure stresses will be transferred to the wire 11 as atensile stress therein. In order to be able to resist the pressurestresses the end pieces 3 and 4 disclosed may be provided in a solidmaterial, for instance a plastic material, such as PVC. Furthermore, thesolid material may be concrete or moulded aluminium. Also othermaterials may be used. It should be noted that the plate heat exchanger1 according to the first embodiment also may be provided with end pieces3, 4 having a construction other than a solid body. For instance, theend pieces 3, 4 may be hollow and filled with a means resisting pressureforces, such as a liquid or support beams.

FIGS. 3-6 disclose a second embodiment of a plate heat exchanger 1according to the present invention. It should be noted that elementshaving a corresponding function have the same reference signs in allembodiments disclosed. As in the first embodiment also the secondembodiment comprises a stack of heat transfer plates 2. Each plate 2 hasan essentially plane extension in the plane X, Z and the plates 2 arecompressed against each other between two end pieces 3 and 4. One 3 ofthe end pieces comprises inlet and outlet means 5 for a first andsecond, respectively, medium carried through the plate heat exchanger 1.

Each end piece 3, 4 comprises a plane plate 12, e.g. a steel plate,forming the inner surface 9 facing the heat transfer plates 2. The inletand outlet means 5 extend through apertures in the plane plate 12 of oneof the end pieces 3. A plurality of support plates 13 are providedperpendicularly, i.e. in the direction Y, to the plane plate 12. As isdisclosed in FIG. 5 each support plate 13, which may be formed by asteel plate, comprises a curved edge surface 14 facing away from theheat transfer plates 2. Thus, in a cross-section plane Y, Z each supportplate 13 has a straight edge line 9 and a convex edge line 14 which e.g.may be oval, elliptic or as in the example disclosed semicircular.Further support plates 15 are provided between each support plate 13 andextending essentially perpendicular to the support plates 13. As isdisclosed in FIG. 5, two such further support plates 15 are providedbetween the middle support plates 13 and three such further supportplates 15 between the outer support plates 13. It should be noted thatthe number of such further support plates 15 of course may be varied andin many cases only one such further support plate 15 between eachsupport plate 13 would be sufficient. Such further support plates 15 maybe formed as individual, loose plates between each pair of supportplates 13 or as a whole plate extending over several support plates 13and being provided with a number of slits 16 extending to about half theheight of the plate 15. In this case, the support plates 13 also haveslits 17 extending to about half the height of the plate 13. By means ofsuch a shape the support plates 13 may, as is disclosed in FIG. 5, beinserted in the further support plates 15 provided against the planeplate 12, in such a manner that the plates 13, 15 are locking each otherin a correct position. Thereby, no further joining, such as welding, isnecessary. However, the plane plate 12, the support plates 13 and thefurther support plates 15 may also be fixed to each other by means ofany suitable joining method such as welding.

In order to compress the plate heat exchanger 1, a compressing member istightable around the end pieces 3, 4 and the heat transfer plates 2. Asis disclosed in FIGS. 3 and 4 the compressing member comprises a numberof U-shaped, curved bolts 18 being provided in pairs around the plateheat exchanger 1 in such a way that the bolts 18 abut the curved edgesurface 14 of the support plates 13 along their curved extension. Thetwo bolts 18 of each pair are provided in a common plane extending inthe directions Y and Z. The bolts 18 of each pair are mutually andreleasably connected to each other in a closed loop by means of twotightable joining members 19 in the form of a nut having a right-handedthread and a left-handed thread. By tightening the nuts 19 the plateheat exchanger 1 may be pretightened by a desired force. Thereby, eachbolt 18 may be provided with a right-handed thread and a lefthandedthread, or one of the bolts 18 of each pair may be provided withleft-handed threads and the other bolt 18 of each pair with right-handedthreads. To ensure that the bolt 18 is not able to slide off the edgesurface 14 of the support plate 13, the further support plates 15 extendupwardly over the support plates 13 in such a way that they prevent alateral movement of the bolt 18, see FIGS. 3 and 4. Possibly, thefurther support plates 15 may be provided with recesses 20 formed in theupper corners in the case that the diameter of the bolt 18 exceeds thethickness of the support plates 13. This embodiment of the compressingmember may of course be combined with the other disclosed embodiments ofthe end pieces, such-as solid end pieces or hollow end pieces.

FIGS. 7 and 8 disclose a further embodiment of a plate heat exchanger 1according to the present invention. The plate heat exchanger 1 comprisesa number of schematically disclosed heat transfer plates 2 compressedbetween two end pieces 3. In FIG. 7 only one 3 of the two end pieces isdisclosed. Each end piece 3 comprises a plane plate 12 abutting the heattransfer plates 2 and a curved body 21 having a convex outer surface 22.The curved body 21 may be formed of a solid body extending over thewhole length X of the plate heat exchanger 1, a curved plate being fixedto the plane plate 12, or be formed of several plane plates extendingperpendicularly in the direction Y from the plane plate 12 and having aconvex edge surface 22. The convex shape may also in this embodiment beoval, elliptic or semicircular. The plate heat exchanger 1 is compressedby a compressing member 23 being formed as a sweep extending around theplate heat exchanger 1 and comprising at least a pair of smoothly bentplates 24 provided around a respective end piece 3 in such a way thatthe end edges of the bent plates 24 adjoin each other with a gap 25therebetween. The curved body 21 may be welded to the plane plate 12 andalso to the bent plate 24. Furthermore, the plane plate 12, as isdisclosed in FIG. 7, may be welded to the bent plate 24. The bent plates24 are kept together by means of at least one joining member 26disclosed in an enlarged sectional view in FIG. 8. Preferably, at leasttwo joining members 26 are provided, one at each side of the plate heatexchanger 1. Each joining member 26 is fixed to each bent plate 24 bymeans of two schematically indicated screws 27. These screws 27 mayextend through holes 26a, 26b in the joining member 26 and be screwed inthreaded holes in the bent plates 24. The joining member 26 comprisesfor each bent plate 24 one or several, in the example disclosed five,protruding ridges extending in the longitudinal direction X of the plateheat exchanger 1 and being provided to engage corresponding recesses 29of the plates 24. Each ridge 28 and recess 29 is provided with abevelled, inclined surface 30 to facilitate the insertion of the ridges28 in the recesses 30. During mounting of the plate heat exchanger 1 theheat transfer plates 2, the plane plates 12 and the bent plates 24 aretightened against each other by means of a tightening member or press.Thereafter, the joining members 26 are screwed to the bent plates 24 bythe screws 26. Thereby, the joining members 26 may be preheated in sucha way that a pretensioning of the plates 24 is obtained when the joiningmembers cool down. The plates 24 may be shaped to extend along the wholelength of the plate heat exchanger 1 in the longitudinal direction X orbe divided in several pairs, which may be equally distributed along thelength of the heat exchanger 1 in the longitudinal direction X.

The present invention is not limited to the embodiments disclosed butmay be modified and varied within the scope of the appended claims.

The compressing member may be shaped in further alternative manners. Forinstance, it may be formed of a plate which preferably is divided in twoparts and which may extend along the whole length X of the plate heatexchanger 1 and be bent around each end piece 3 and 4. The end pieces 3and 4 are compressed together with the outer plates against each otherin a suitable tightening device, in such a way that the end edges of theplates abut each other. Thereafter, these end edges are joined togetherby means of a suitable method such as welding.

Instead of a compressing member comprising a pair of bolts 18 mutuallyconnected to a loop by means of the nuts 19, the compressing member maycomprise one bolt extending in a loop around the end pieces 3, 4 and thestack of heat transfer plates 2. In this case the ends of said one boltare connected to each other by one nut 19 having one left-handed threadand one right-handed thread, in such a manner that the bolt is closelyabutting the curved outer surfaces of the end pieces 3, 4.

Furthermore, the compressing member may be formed of one or severalbands being extended around the plate heat exchanger 1. Such bands maybe applied by means of a tightening device which tightens the bandaround the plate heat exchanger 1 and deforms the material in both endsof the band in such a way that the ends are fixed to each other. As inthe case with the plate-shaped compressing member, it may beadvantageous to provide two bands provided in pairs, each band extendingaround a respective end piece 3, 4 and being tightened at each side ofthe plate heat exchanger 1. In such a way one may prevent differenttightening forces at each side of the plate heat exchanger due tofriction.

It should be noted that the compressing members 11, 18, 24 may beprovided to extend around the plate heat exchanger 1 at only one orseveral locations in order to strengthen relatively weak portions, suchas the area around the inlet and outlet means 5, respectively.

Each end piece may comprise a plane plate abutting the heat transferplates 2 and a curved plate being fixed to the plane plate and formingthe curved outer surface abutted by the wire, the bands, the bolts etc.In order to increase the strength with respect to pressure forces andprevent that the curved plate is deformed, a means resisting pressureforces may be provided between the plane plate and the curved plate. Onesuch means may for instance be a liquid, support beams or concrete.

What is claimed is:
 1. A plate heat exchanger (1) comprising a stack ofheat transfer plates (2) provided between two end pieces (3, 4) and eachhaving an essentially plane extension, each end piece (3, 4) having aninner surface facing said heat transfer plates (2) and an outer surface(10, 14, 22) facing away from said heat transfer plates (2) andextending from one side to another of the end piece (3, 4), the plateheat exchanger (1) being compressed by means of at least one member (11,18, 24) extending around the end pieces and the heat transfer plates insuch a manner that said member abuts said outer surface (10, 14, 22) ofeach end piece (3, 4) in order to prevent the retreat of the end piecesfrom each other, wherein said outer surface (10, 14, 22) of each endpiece (3, 4) is continuously curved from said one side to another insuch a manner that the end piece has a convex shape in a cross-sectionalong a first plane (Y, Z) crossing said sides and being perpendicularto the essentially plane extension of the heat transfer plates (2) andthe curved outer surface (10, 14, 22) in the proximity of an edgebetween said inner surface (9) and said outer surface (10, 14, 22) isshaped in such a manner that a tangential plane (X, Y) of said outersurface is essentially perpendicular to the essentially plane extensionof the heat transfer plate (2).
 2. The plate heat exchanger according toclaim 1, wherein that the compressing member (11, 18, 24) comprisesjoining means (19, 26) provided to releasably tighten the compressingmember around the end pieces (3, 4) and the heat transfer plates (2). 3.The plate heat exchanger according to claim 2, wherein that said joiningmeans (19) is provided to enable adjustment of the compressing force ofthe compressing member (18).
 4. The plate heat exchanger according toany claim 1, wherein the compressing member (11, 18, 24) comprises atleast one wire-, bar-, band- or plate-like member extending around theend pieces (3, 4) and the heat transfer plates (2).
 5. The plate heatexchanger according to claim 1, wherein the compressing member comprisesat least one bolt (18) extending in a loop in such a manner that it isclosely abutting at least one of the curved outer surfaces of the endpieces (3, 4).
 6. The plate heat exchanger according to claim 5, whereinthe compressing member comprises at least a pair of said bolts (18)mutually connected to a loop and being curved in such a way that theyare closely abutting the curved outer surfaces (14) of the respectiveend pieces (3, 4) in a common plane.
 7. The plate heat exchangeraccording to claim 2, wherein said joining means comprises a nut (19)having a right-handed thread and a left-handed thread and being screwedonto opposite bolt ends.
 8. The plate heat exchanger according to claim1, wherein the compressing member comprises a wire (11) being wound in ahelical coil about the end pieces (3, 4) and the heat transfer plates(2).
 9. The plate heat exchanger according to claim 8, wherein thehelical wire coil is wound in such a manner that each round of the wire(11) is abutting the adjoining wire round.
 10. The plate heat exchangeraccording to claim 1, wherein the compressing member comprises a plate(24) extending around the end pieces (3) and the heat transfer plates(2).
 11. The plate heat exchanger according to claim 10, wherein saidcompressing plate (24) is divided into two parts, each part extendingaround a respective end piece (3) in such a way that each end edge ofone part is adjacent to an end edge of the other part, and whereinadjacent end edges of said parts (24) are joined to each other byjoining means.
 12. The plate heat exchanger according to claim 1,wherein each end piece (3, 4) comprises a plane plate (12) forming saidinner surface (9).
 13. The plate heat exchanger according to claim 12,wherein each end piece (3, 4) comprises a support plate (13, 21)disposed on the plane plate (12) and having a curved edge surface (14,22).
 14. The plate heat exchanger according to claim 13, wherein thesupport plate (13, 21) extends essentially perpendicularly to the planeplate (12).
 15. The plate heat exchanger according to claim 14, whereinseveral support plates (13) are provided spaced from each other and thata further support plate (15) extends essentially perpendicular to thesupport plate (13) in order to support the support plates (13) inlateral direction.
 16. The plate heat exchanger according to claim 1,wherein said convex shape is essentially semicircular.
 17. The plateheat exchanger according to claim 1, wherein said compressing member(11, 18, 24) extends around the plate heat exchanger (1) in acircumferential direction lying in a plane (Y, Z) being perpendicular tothe essentially plane extension of the heat transfer plates (2).